Floating nozzle and shroud construction for gas turbine



Aug. 12, 1969 R. w. VERSHUREE, JR 3,460,806

FLOATING NOZZLE AND SHROUD CONSTRUCTION FOR GAS 'TURBINE Filed Sept. 8,1967 2 Sheets-Sheet 1 ATTORNEY 12, 1959 R. w. VERSHURE, JR 3,460,806

FLOATING NOZZLE AND SHROUD CONSTRUCTION FOR GAS TURBINE Filed Sept. 8.1967 2 Sheets-Sheet z INVENTOR. ROY w. VERSHUREJR.

ATTORNEY United States Patent 3,460,806 FLOATING NOZZLE AND SHROUDCONSTRUC- TION FOR GAS TURBINE Roy W. Vershure, In, Phoenix, Ariz.,assignor to The Garrett Corporation, Los Angeles, Calif., a corporationof California Filed Sept. 8, 1967, Ser. No. 666,407 Int. Cl. Ftlld 1/08,9/02, 25/26 U.S. Cl. 253-39 8 Claims ABSTRACT OF THE DISCLOSURE Thisfloating nozzle and shroud for a centripetal gas turbine includes anintegral nozzle structure having spaced rings connected bycircumferentially spaced, angularly disposed vanes, the wall thicknessof the rings, vanes and shroud being substantially equal and thestructure being loosely arranged in an open annular space between agas-receiving torus and turbine wheel chamber. The nozzle-receivingspace is formed by bolting a combined shroud and exhaust tube to aflange on the frame with spacers therebetween, the bolts and spacersextending through openings formed in the vanes. One ring of the nozzlestructure is extended inwardly to form a shroud at the back of theturbine Wheel. The loose mounting permits thermally induced expansionand contraction without stress or strain.

Summary This invention relates generally to turbomachinery and isdirected more particularly to a gas turbine engine of the type having acentripetal wheel. Still more particularly, the invention is centeredaround the mount ing of the nozzle and shroud portions of the gasturbine engine, the primary objective being to so support these elementsthat stress or strain due particularly to expansion and/or contractionresulting from temperature variations will be avoided. The life of theengine will thus be extended.

Heretofore, in engines of this type the nozzle member which is usuallyof relatively light weight and thin structural section has been rigidlyconnected to adjacent portions, such as the engine casing or frame, orother parts of heavier construction. All of these parts are exposed toquite high temperatures during engine operation, Such high temperaturescause the parts to expand. When engine operation is discontinued theparts cool. Some parts, such as the nozzle vanes and other adjacentparts of thin section being exposed to cold air since the flame in thecombustor has been extinguished, cool rapidly. Other parts which may beof heavier cross section and not directly exposed to the cool air willcool more slowly. With the former parts directly connected to thelatter, high stress or strain is introduced which causes the cracking orbreaking and premature destruction of the thinner parts. Replacementthen becomes necessary.

To avoid the above difliculties, the present construction has beenproposed. It includes the features of forming the nozzle integrally andof relatively light construction but mounting it so that it is free fromdirect or positive connection with adjacent parts of heavierconstruction. By so supporting the nozzle it is free to expand andcontract at diflerent rates than the adjoining elements and may do so"ice without the introduction of stress or strain. When the combustorflame is extinguished and cool air suddenly contacts the nozzle vanesand adjacent structure, contraction thereof can take place withoutopposition from the still expanded supporting or gas flow confining anddirecting members.

Another object of the invention is to provide a centripetal gas turbineengine with a nozzle structure having a pair of side rings withgas-directing vanes extending therebetween, and supporting means for thenozzle structure, the supporting means forming a space for relativelyloosely receiving the nozzle structure whereby the latter is free tofloat to a limited extent and expansion and/ or contraction can takeplace without opposition. The mounting obviously prevents such excessivemovement of the nozzle structure that the operation of the turbine wheelwould be opposed.

Still another object of the invention. is to provide a centripetal gasturbine engine with a nozzle, shroud, and gas-receiving torusconstruction in which one wall of the torus is formed with an openingfor the relatively loose reception of a portion of the nozzle and itssupport, the support also being formed with a space for the relativelyloose reception of the nozzle per se, this construction minimizing thepossibility of temperature induced eX- pansion and contraction stressesand strains being transmitted from one part to another.

A more specific object is to construct a gas turbine engine having anozzle construction which includes a pair of integrally formed annularplates spaced by angular vanes, 21 support member mounted on the enginecasing and having a plate to which is bolted one flange of a combinedshroud and exhaust gas outlet tube, a plurality of spacers beingdisposed between the shroud flange and support plate to form a space'for the loose reception of the nozzle structure; the space permitslimited movement of the nozzle structure to compensate for expansion andcontraction caused by wide temperature variations between operating andshutdown conditions of the engine.

Other objects and advantages of the invention will be apparent from aperusal of the following description of one embodiment of the inventionillustrated in detail in the accompanying drawings.

Drawings FIG. 1 is an axial sectional view of a portion of a centripetalgas turbine engine showing the turbine wheel and adjacent nozzle andshroud construction embodying the invention;

FIG. 2 is a vertical transverse sectional view taken through the nozzlemechanism on the plane indicated by the line II--II of FIG. 1;

FIG. 3 is a detail fragmentary sectional view on an enlarged scale takenthrough a portion of nozzle mechanism and adjacent structure to show oneof the nozzle mounting features; and I FIG. 4 is also an enlarged detailsectional view taken on the plane indicated by the line IV-IV of FIG. 3.

Description More particular reference to the drawing will show that thegas turbine engine selected to illustrate the invention includes acompressor portion A and a turbine portion B. Both of these portions aredisposed in an engine casing C formed of a plurality of suitable parts.The casing has spaced bearings 10 and 11 to rotatably support a shaftassembly 12 to which is suitably affixed a compressor rotor 13 and aturbine wheel 14. This arrangement provides for the rotation of therotor, the turbine wheel and the shaft as an integral unit.

The casing also supports a shroud 13A for the compressor rotor so thatupon rotation of the latter, air is drawn into the passages in the rotorand discharged outwardly from the periphery of the rotor through adiffuser passage 15 to a plenum 16 formed by a part of the casing C.Within the plenum 16 the casing is provided with a gas-receiving torus17 into which gases resulting from mixing and burning fuel with thecompressed air in a combustor (not shown) are discharged. These gasesflow through the torus to a nozzle structure 18 formed in accordancewith the present invention.

The nozzle structure 18 directs the hot gases against the blades of theturbine wheel to effect rotation of this element and the other partssecured thereto. Nozzle structure 18 includes front and rear annularplates 20, 21 and angularly inclined vanes 22 integrally formed with theplates. The vanes are circumferentially spaced and cooperate with theplates to provide passages through which the gases flow to the turbinewheel. Torus 17 partly surrounds the nozzle structure and a combinedperipheral wheel shroud and exhaust tube 23 the outer end of which issecured to the casing as at 24, the torus also having one end wallsecured to the casing adjacent the end of tube 23. The other end wall 25of the torus has an opening formed therein to receive a portion of thenozzle structure. Peripheral wheel shroud 23 has a flange 26 providedwith an annular recess 27 to receive the annular front plate 20 of thenozzle structure. It will be noted from FIGS. 2 and 4 that the plates20, 21 and vanes 22 have openings 28 for bolts 30 employed to secureflange 26 of shroud 23 to a flange 31 formed on a bearing and nozzlesupport bracket 32 which is in turn secured to the engine casing, as at33.

The openings 28 also receive elongated spacers 34 the ends of whichengage flanges 26 and 31 and serve to limit the spacing therebetween toa distance slightly exceeding the front-to-back measurement of thenozzle structure, i.e., the plates 20, 21 and vanes 22. Thisconstruction confines the nozzle structure but permits a predeterminedamount of growth both axially and radially of the assembly toaccommodate dimensional changes due to temperature variations.

Rear annular plate 21 is extended inwardly, as at 35, to provide a rearshroud for the turbine wheel which is relieved, as at 36, to conform tothe shroud. It will be noted that the hub 37 of the wheel terminatesimmediately within the inner edge of the shroud to inhibit flow of gasesto the back of the wheel. By forming rear shroud on plate 21 anddisposing it in closely spaced relation to the back edges of the wheelblades, the front surface of the shroud is aligned and substantiallyfaired into the curved surface of the wheel between the vanes. Thisarrangement guides the hot gases and makes them flow smoothly withoutinterruption from the nozzle through the passages between wheel bladesand along the wheel hub. Impingement of the hot gases on the edges ofthe hub between the blades cannot occur and localized hot spots as aresult thereof are prevented.

Attention is called to the fact that the outer surfaces of the plates20, 21 are relieved to make them of substantially uniform thicknessthroughout whereby all parts thereof will heat up and cool off at thesame rate and therefore will expand and contract uniformly.

In FIG. 3 it will be noted that flange 31 and plate 21 are disposed inthe opening in torus end wall 25 which opening is of a size suflicientto permit relative axial movement between the nozzle and shroud assemblyand the torus. The wall 25 has a ring 38 bolted thereto to preventexcessive movement in one direction. This ring 38 also partially closesthe space between the edge of the opening and the flange 31 to inhibitfluid flow therethrough.

When the gas turbine engine is in operation, compressed air will bereceived by the plenum 16. This air is supplied to the combustor (notshown) where fuel is mixed therewith and burned to provide hot gases.These gases are conducted by the torus 17 to the nozzle structure 18which directs them against the turbine wheel blades to rotate the wheel.It will be obvious that the hot gases contacting the nozzle plates andvanes, the shrouds, the exhaust tube, and the wheel will cause thetemperatures of these elements to increase, and consequently theelements will expand. By reason of the extra space between flanges 26and 31 the nozzle structure can expand without opposition. The clearancebetween the wheel blades and shrouds 23 and 35 is so calculated that nointerference to wheel rotation will take place.

When the flow of fuel to the combustor is interrupted to effect ashutdown of the engine, relatively cool compressor discharge air willengage the nozzle structure and adjacent components. This cool air willreduce the temperatures of these elements. Due to the relatively thinwall construction of the nozzle parts they will cool faster and contractmore rapidly than the heavier adjacent parts. Once again, it will beobvious that by reason of the floating construction of the nozzlestructure the contraction will be unopposed and no stress or strain willbe encountered. There will therefore be no cracking, breakage, or otherpremature failure of these parts. The active life of the engine is thusprolonged.

I claim:

1. In a gas turbine engine of the type having a casing, a turbine wheel,and a gas-receiving torus assembly secured to the casing and surroundingsuch wheel, said torus having an opening in an end wall adjacent thewheel, the combination comprising:

(a) nozzle supporting means mounted in said casing and having a ringlikeflange substantially closing the opening in the wall of the torusassembly, said supporting means also having a wheel periphery shroudwith a flange secured to said ringlike flange in a manner to form aspace therebetween;

(b) a nozzle assembly disposed for limited movement in the space betweensaid flanges, said assembly being free from direct connection with anyadjacent structure and having annular plates integrally formed at theends of circumferentially spaced angular vanes, said annular plates andvanes being of substantially equal thickness to secure uniform rates ofthermal expansion and contraction throughout said nozzle assembly.

2. The gas turbine engine nozzle and shroud combination of claim 1 inwhich said nozzle-supporting means has bolts to connect said ringlikeflange and said peripheral shroud flange and spacers adjacent said boltsto provide a nozzle-assembly-receiving space between the flanges.

3. The gas turbine engine nozzle and shroud combination of claim 1 inwhich one of said annular plates is extended radially inwardly toprovide a ringlike back shroud for the turbine wheel.

4. The gas turbine engine nozzle and shroud combination of claim 1 inwhich the supporting means is secured to the casing at one side of andin spaced relation from the torus wall having the opening for thesupporting means flange, the end wall of the torus opposite that havingsuch opening being attached to the engine casing, and the shroud memberadjacent the peripheral portion of the turbine wheel being secured tothe engine casing adjacent to the location of attachment of the torusthereto.

5. The gas turbine engine nozzle and shroud combination of claim 3 inwhich the back side of the turbine wheel is shaped to closely fit saidshroud with a predetermined amount of clearance space therebetween.

6. The gas turbine engine nozzle and shroud combination of claim 3 inwhich the ringlike shroud at the back of the turbine Wheel is normal tothe axis of rotation thereof, the adjacent portion of said wheel beingshaped to closely conform to said shroud with a predetermined amount ofclearance space therebetween.

7. The gas turbine engine nozzle and shroud combination of claim 3 inwhich the hub of the turbine wheel terminates adjacent to the inner edgeof said ringlike shroud.

8. The gas turbine engine nozzle and shroud combination of claim 2 inwhich the nozzle plates and some of the vanes are provided withregistering openings for the reception of the fastening means employedto connect the flanges of said supporting means and spacing meansdisposed between the flanges of the peripheral shroud and supportingmeans to provide limited clearance for said nozzle means.

References Cited UNITED STATES PATENTS 2,529,880 11/1950 McClure.3,014,694 12/1961 Paul et a1. 3,072,380 1/1963 Henning. 3,106,38110/1963 Leins 253 -55 3,112,096 11/1963 Lazo et a1. 253-55 3,199,2948/1965 Hagen 253-55 X 3,366,365 1/1968 Rizk. 3,384,345 5/1968 Neath eta1.

EVERETTE A. POWELL, Primary Examiner US. Cl. X.R. 253-55

